Cigarette making machines commonly operate by forming a continuous rod which is then cut into discrete lengths by a cut-off device while the rod is being supported by what is commonly termed a xe2x80x9cledgerxe2x80x9d. Such ledgers commonly have an oscillating motion and contact the rod only at a top-dead-centre position of the ledger, but refinements have been proposed whereby the part of the ledger which supports the rod moves with a more nearly linear oscillating motion. Oscillating ledgers, however, tend to be noisy. With a view to reducing the noise there have been proposals involving purely rotary motions whereby the part of the ledger which supports the rod during cutting is momentarily in contact with the rod; this has a disadvantage in that the rod-supporting part cannot be tubular, but must instead be U-shaped so as to be able to move towards and away from the rod.
Another possibility is described in our British patent No. 2108820, in which FIG. 1 shows a ledger whereby linear motion of a rod-supporting part is produced by pivotally connecting opposite ends of that part to two devices each consisting of an internal gear within which orbits an external gear which is half the diameter of the internal gear. This arrangement has a number of practical disadvantages, amongst which is the fact that it does not lend itself to rod length adjustment.
The above-mentioned patent also shows, in FIG. 3, a ledger comprising mainly rotary parts but which nevertheless produce linear motion of the rod-supporting part, and allows for changes in the rod length.
In general terms such a ledger (the reference letters being as used in this specification) comprises a rod-supporting part which is pivotally mounted on two linear motion devices each comprising a fixed gear (A), a second gear (B) which is preferably smaller than the fixed gear and which orbits about the axis of the fixed gear, and a pair of connected coaxial gears (C) and (D) of different diameter which also orbit about the axis of the fixed gear and which mesh respectively with the fixed gear and first orbiting gear (B), such that the effective gear ratio between the fixed gear (A) and the first orbiting gear (B) via the other two gears is 2:1, the rod supporting part being pivotally connected to the first orbiting gear (B) or to a crank connected thereto. The present invention is concerned with various improvements to such a ledger.
The distance between the axis (Ac) of the fixed gear and the axis (Bc) of the first orbiting gear should be equal to the distance between the axis (Bc) of the first orbiting gear and the pivot axis (P) by which the rod supporting part is pivotally connected to the first orbiting gear. These distances can be changed in order to change the rod length. The rod length (i.e. the intervals between successive cuts of the continuous rod) is related to the distance AcBc and BcP as follows:
AcBc=BcP=Rod Length divided by 4xcfx80
The rod length referred to is twice the length of the tobacco-filled rod of each cigarette; double length portions are usually cut by the cut-off of the cigarette making machine, and are subsequently cut into two equal portions in the associated filter attachment machine. For example, for a rod length of 140 mm (for average-length cigarettes having a 70 mm tobacco rod) the distance AcBc and BcP would each be 11.14 mm.
The distances AcBc and BcP may in theory be made adjustable, as described in our above-mentioned patent, but only with difficulty. Instead, according to one aspect of the present invention, an assembly comprising the parts determining those distances is designed to be interchangeable. Those parts which need to be changed in order to achieve a different rod length are described below in the specific description with reference to the drawings.
According to another aspect of the present invention, the rod-supporting part comprises two members having adjacent ends pivotally connected to one another and being pivotally connected at their other ends to the respective linear motion devices. The two members are preferably substantially identical, being mirror images of one another, each having a tube-like portion through which the cigarette rod is arranged to pass and by which the rod is supported, the cut-off knife being arranged to pass between the two tube-like portions during each cutting operation.
This aspect of the invention avoids the generation of excessive bending stresses in the rod supporting part which can occur if the rod supporting part is in one piece.
Other aspects of this invention include, for example, the provision described below for setting up each linear motion device by means of a jig following the introduction of change parts in order to change the rod length.
An example of a ledger including all aspects of this invention is shown in the accompanying drawings.